Clinical findings in untreated classic phenylketonuria

Phenylketonuria (PKU) is usually detected in the neonatal period with the use of Guthrie test. We present a 3-year-old girl whose diagnosis of PKU was established at 21/2 years of age. She presented with severe learning disability, poor behavior control, and aphasia. A urine phenylpyruvic acid test using ferric chloride done in Paraguay at 5 days of age was normal. Physical examination was remarkable for a very light skin color and red-white hair. The patient's mother has dark skin and black hair an the father has light skin and brown hair. Neurological examination revealed mental retardation and hyperactivity. A low phenylalanine diet was started and her behavior and vocabulary improved. This case report describes the clinical manifestations of untreated classic PKU and confirms that ferric chloride urine test has a low sensitivity and should not be used to exclude PKU.